The present invention relates generally to refrigeration systems (including refrigerators, air conditioners, heat pumps and water coolers/chillers) and, more specifically, to a means and method for increasing the efficiency of a refrigeration system that is not operating at peak efficiency.
A refrigeration system typically consists of four major components connected together via a conduit (preferably copper tubing) to form a closed loop system. Referring to FIG. 1, a conventional refrigeration system 500 is illustrated. The four major components are a compressor 52, a condenser 54, an expansion device 56 and an evaporator 58. A refrigerant circulates through the four components via the conduit 59 and will have its pressure either increased or decreased, and its temperature either increased or decreased by the four components. The refrigerant is continuously cycled through the refrigeration system. The main steps in the refrigeration cycle are compression of the refrigerant by the compressor 52, heat rejection of the refrigerant in the condenser 54, throttling of the refrigerant in the expansion device 56, and heat absorption of the refrigerant in the evaporator 58. This process is sometimes referred to as a vapor-compression refrigeration cycle. The compressor 52 includes a motor (usually an electric motor) and provides the energy to keep the refrigerant moving within the conduits and through the major components.
The vapor-compression refrigeration cycle is the principle upon which conventional air conditioning systems, heat pumps, and refrigeration systems are able to cool and dehumidify air in a defined volume (e.g., a living space, a vehicle, a freezer, etc.) The vapor-compression cycle is made possible because the refrigerant is a condensible gas and exhibits specific properties when it is placed under varying pressures and temperatures.
During the refrigeration cycle, the refrigerant enters the compressor as saturated vapor and is therein compressed to a very high pressure. The temperature of the refrigerant increases during the compression step. The refrigerant leaves the compressor as superheated vapor and enters the condenser.
A typical condenser comprises a single conduit formed into a serpentine-like shape so that a plurality of rows of conduit are formed parallel to each other. Metal fins or other aids are usually attached to the outer surface of the serpentine conduit in order to increase the transfer of heat between the superheated refrigerant vapor passing through the condenser and the ambient air. Heat is rejected from the superheated vapor as it passes through the condenser and the refrigerant exits the condenser as a saturated or subcooled liquid.
The expansion device reduces the pressure of the liquid refrigerant thereby turning it into a saturated liquid-vapor mixture, which is throttled to the evaporator. In order to reduce manufacturing costs, the expansion device is typically a capillary tube in small air conditioning systems. The temperature of the refrigerant drops below the temperature of the ambient air as it passes through the expansion device. The refrigerant enters the evaporator as a low quality saturated mixture comprised of approximately 20% vapor and 80% liquid. (xe2x80x9cQualityxe2x80x9d is defined as the mass fraction of vapor in the liquid-vapor mixture.)
The evaporator physically resembles the serpentine-shaped conduit or coils of the condenser. The evaporator also includes fins or other means of increasing the surface area of the serpentine-shaped conduit. Ideally, the refrigerant n the evaporator completely evaporates by absorbing heat from the defined volume to be cooled (e.g., the interior of a refrigerator) and leaves the evaporator as saturated vapor at the suction pressure of the compressor and reenters the compressor thereby completing the cycle.
The efficiency of a refrigeration cycle is traditionally described by an energy-efficiency ratio (EER). It is defined as the ratio of the heat absorption from an evaporator to the work done by a compressor.   EER  =            Heat absorption from evaporator              Work done by compressor      
In a typical air conditioning system, the refrigeration cycle has an EER of approximately 3.0 (kw/kw) or 10.2 (Btu/hr/kw). As can be seen from the EER equation, the efficiency of the refrigeration system increases by decreasing the work performed by the compressor.
In recent years, compressor manufacturers have made strides in improving the overall efficiency of a refrigeration system by improving the efficiency of the compressor. Two important advancements in compressor efficiency were achieved with the development of scroll compressors and with the improvement in control circuitry of the compressors.
The motors in previous compressors ran at a single speed (usually at a very high speed). Both inverter compressors and digital scroll compressors include circuitry that allows the compressor motor to vary its speed depending on load conditions. By designing a control system that allows the compressor motor to increase speed during high load periods and to decrease speed during low load periods, the overall work done by a variable-speed compressor is reduced, thereby increasing the overall efficiency of the refrigeration system. (It should be noted that fans driven by electric motors are usually associated with the condenser and the evaporator for drawing air over and/or through the respective serpentine-shaped coils. The electric fan motors may also be variably-speed controlled to correspond with the output of the compressor and further increasing the overall efficiency of a refrigeration system.)
When the compressor motor is operating at a very high speed (and usually when it operates at a very slow speed) versus an optimum speed, the efficiency of the refrigeration system is not at its peak. Therefore, even though variable speed compressor motors may increase the overall efficiency of a refrigeration system, there are certain periods of operation where the efficiency may still be increased.
In addition, the U.S. Department of Energy has expressly identified the problem of incorrect charge of refrigerant circulating in refrigeration/air conditioning systems as a major source of inefficiency. The amount of refrigerant in a refrigeration system is not optimized (i.e., usually low or insufficient) primarily because the refrigeration technicians undercharge the system during installation or do not properly read the gauges during the maintenance of a refrigeration system. A refrigeration system that is undercharged will not perform up to its specified EER claims and may also severely decrease the life-span of a compressor.
Vortex tubes are well known. Typical vortex tubes are designed to operate with non-condensible gas such as air. A typical vortex tube turns compressed air into two air streams, one of relatively hot air and the other of relatively cold air. A common application for prior vortex tubes is in air supply lines and other applications which utilize gas under a high pressure.
A vortex tube does not have any moving parts. A vortex tube operates by imparting a rotational vortex motion to an incoming compressed air stream; this is done by directing compressed air into an elongated channel in a tangential direction.
The present invention addresses the issue of performance degradation in a refrigeration system due to an insufficient charge of refrigerant or during periods of high load in a variable speed compressor (e.g., inverter compressor or digital scroll compressor). For example, when an inverter compressor is used in a small air-conditioning refrigeration system, the degree of the sub-cooling in the refrigerant after it exits the condenser decreases from its optimum value of 11 degrees Celsius (C) to about 5-6 degrees Celsius. As a result, the EER of this refrigeration system typically decreases from 10.0 to 8.0 (Btu/hr/kW). A similar decrease in efficiency is found in refrigeration systems utilizing digital scroll compressors.
Also, when there is a loss of refrigerant or an insufficient charge of refrigerant, the degree of the sub-cooling in the refrigerant after condensing by the condenser decreases from its optimum value of 11 degrees C to about 5-6 degrees C for a small air-conditioning refrigeration system. Again, the EER decreases from an optimum value of about 10.0 to about 8.0 (Btu/hr/kW) for this small air-conditioning/refrigeration system.
The present invention is designed to recover the maximum efficiency of a refrigeration, air conditioning or heat pump system (collectively referred to as refrigeration systems) during periods when it is not operating at peak efficiency. The increase in the efficiency is achieved by assisting in the conversion of the refrigerant from vapor to liquid at specific points in the refrigeration cycle.
In many present day refrigeration systems, an inverter compressor or a digital scroll compressor is used to increase the overall efficiency of the refrigeration system. However, there are periods when the efficiency of the refrigeration system is lower than at other periods.
In a preferred embodiment of the present invention, a first vortex generator is placed in the condenser about one-quarter of the way in from the inlet of the condenser (i.e., either in the serpentine tubing of the condenser or by splitting the condenser into a xc2xc length section and a xc2xe length section). A vortex generator is designed to work specifically with condensible vapors such as refrigerants.
Ideally, the vortex generator is placed at a point where the desuperheating is completed (i.e., at a point where the superheated vapor becomes saturated vapor in whole or in part). The vortex generator produces liquid refrigerant and further increases the temperature of the vapor refrigerant thereby reducing the size of the condenser and decreasing the head pressure of the compressor. As a result, the compression ratio decreases, and the work required by the compressor is reduced, thus increasing the efficiency of the refrigeration cycle.
In an alternate embodiment, a vortex generator is placed between the expansion device and the evaporator in order to increase the percentage of refrigerant entering the evaporator as a liquid. Since the heat absorption from the evaporator occurs through the evaporation of the liquid refrigerant, the increase in the percentage of the liquid refrigerant entering the evaporator increases the efficiency of the refrigeration cycle and reduces the size requirements of the evaporator.
In addition to the one or two vortex generators described above, other embodiments may include a second (or third if both of the aforementioned vortex generators described above are used) vortex generator placed between the evaporator and the compressor in order to increase the percentage of refrigerant entering the compressor as a vapor.